Mesonychoteuthis Hamiltoni

If one species could claim the title of being a real life mythical beast, then that honour would surely go to Mesonychoteuthis hamiltoni: the colossal squid. With its enormous eyes, long tentacles lined with barbed suckers and triple-tipped hooks, this squid certainly sounds like something from ancient mythology. Yet unlike other monsters of legend, the colossal squid really exists, and it is a truly awe-inspiring species.

Physical Appearance

From the few examples of the colossal squid that have been recovered for study, it is estimated that the species may reach 14m in length when fully grown, though scientists suggest a slow rate of development reduces the chance of individual animals reaching this size. In terms of mass the adult squid can weigh as much as 750kg. While the similarly sized giant squid is known to grow longer, its elongated shape and less dense body means that it is a smaller species overall, making the colossal squid not only the most massive squid, but also the largest invertebrate, on the planet.

That is not the only remarkable record that this squid holds though, as it is also the owner of the world's largest eyeballs, too. An eyeball recovered from a captured squid had a diameter of 27cm; measured after a freezing and thawing process which had led to shrinkage. It is estimated that the same eyeball could have measured up to 40cm while the animal was alive.

The squid is known to prey upon large fish such as the Antarctic and Patagonian toothfish, demonstrated by instances in which the squid has been netted by fishing trawlers alongside these other species - including one squid that was discovered still feeding on a line-caught toothfish as it was landed.

It is also theorised that the squid feeds on smaller, bioluminescent squid found in the same areas of the ocean but, while its enormous ocular organs may play some role in hunting at depths, it is believed that its sensitive eyes are primarily used for detecting predators. Because, despite its fearsome size, the colossal squid is a favoured source of food for many large ocean predators.

Habitat, Food and Predation

Perhaps the most intriguing fact about this incredible animal is just how little we actually know about it compared to many of our other giant species. Much of our understanding of the species has been learned from only a handful of specimens - these are often immature or incomplete animals, and usually discovered by chance. In fact, despite its enormous size, the depths of the squid's habitat meant that it remained undocumented until 1925.

It was through predation that the species originally came to human attention, when the first remnants of the animal were discovered in the stomach of a sperm whale. And it is through predation that we continue to learn about its behaviour and habitat. From beaks found within sperm whale stomachs, scientists have determined that the squid inhabits depths of at least 2.2km. It is believed that the squid accounts for as much as 77 per cent of the whale's biomass intake. Happily, from this rate of predation, it is believed that this remarkable animal is not yet an endangered species.

Not only has this research enabled conservationists to determine the numbers of this rarely-sighted creature, the data has also provided a greater understanding of this elusive creature's distribution, too. The giant of the southern ocean inhabits the icy waters around Antarctica, with a wider habitat that stretches more than a thousand kilometres north, to reach the southern shores of south America and New Zealand.